Reactors used for chemical reactions are broadly classified into two types. The first type is a mixing-tank type reactor, which has a perfect mixing characteristic such that materials to be reacted (hereinafter referred to as raw materials) are fully mixed in a mixing tank so as to have the same composition and temperature. In general, the mixing-tank type reactors are separated into plural compartments and agitation is performed in each compartment. One example of the reactors is disclosed in an unexamined published Japanese patent application No. 2003-316074 (JP2003-316074A). The second type is a tube type reactor, in which raw materials are fed through a tube without agitation so as to be reacted.
Tube-type reactors have the advantage of having low costs because agitation is not necessary. However, tube-type reactors tend to cause a short-path problem in that when a filler such as catalysts is not present in the tube, the flow speed of the raw material in a central portion of the tube is faster than that in a portion near the inner wall of the tube, and therefore the residence time of the raw materials in the central portion of the tube shortens, resulting in decrease of the reaction rate. In order to obtain a sufficient residence time of the raw materials in such tube-type reactors, it is necessary to enlarge the reactors. In addition, tube-type reactors have another disadvantage such that it is difficult to allow a raw material to maintain steady flow in a tube due to change of the density of the heated raw material.
In order to keep the residence time of a raw material constant at any points on a cross-sectional surface of the tube perpendicular to the central axis of the tube, it is considered to use a technique using a perforated plate tower having plural perforate plates, which is disclosed in JP H10-015381A and which is used for gas-liquid reactions. It is known that when a fluid passes through a perforated plate having a constant aperture ratio, the flow speed of the fluid reaches a constant speed before and after the perforated plate. However, even when this technique is used, the flow speed of a raw material in a central portion of the tube is still faster than that in a portion near the wall of the tube.
In attempting to enhance the effect of the technique using a perforated plate tower, JP H07-060107A discloses a technique using a perforated plate which has larger aperture ratio in a portion of the plate near the wall of the tube than that in the central portion of the plate. However, this technique tends to cause a problem in that a raw material stays in several portions of the tube without being smoothly flown in the tube. In particular, when a slurry including a solid component is used as the raw material, a deposition problem in that a large amount of deposition of the solid component is formed in the tube, and therefore it is necessary to frequently clean the tube is caused.
Recently, polymerized toners are used for electrophotography. Such polymerized toners are typically prepared by using such a reactor while using a slurry including a solid component as the raw material. For example, JP H11-133665 discloses a toner production method which uses a slurry including a liquid including an organic solvent and an aqueous medium, and a solid component including a polyester prepolymer having an isocyanate group and which performs a polymerization process in which the prepolymer and an amine are subjected to a polyaddition reaction in the liquid.
Conventional polymerized toner production methods include heating raw materials to polymerize a polyester resin having a desired molecular weight distribution, which is used as a binder resin of the toner, and to prepare a toner having a good combination of low temperature fixability and offset resistance.
Although the heating process of the conventional polymerized toner production methods can be easily used for the polycondensation reaction for forming a polyester, the methods cannot be easily used for a reaction of a slurry including a liquid including an organic solvent and an aqueous medium, and a solid component unless various production conditions are properly controlled. Namely, it is necessary to carefully optimize the conditions such as reaction temperature and maturing temperature when preparing a polymer.
For these reasons, the inventors recognized that there is a need for a toner production method using a reactor, which can prepare a polymerized toner without causing the short path problem and the deposition problem, and without specifying the heating temperature in detail, even when a slurry including a solid component is used as the raw material.